Preheat neutralizing circuit for fluorescent lamps



June 30, 1953 KElFFER ETAL 2,644,107

7 PREHEAT NEUTRALIZING CIRCUIT FOR FLUORESCENT LAMPS Filed Nov. 25. 19492 Sheets-Sheet l 1 f2 /Z I I? lnven kors: Raymond L. Kei=f-+er1 B weLemmers, b5 W Their" A'iriorneg.

June 1953 R. 1.. KEIFFER ETAL 2,644,107

PREHEAT NEUTRALIZING CIRCUIT FOR FLUORESCENT LAMPS Filed Nov. 23, 1949 2Sheets-Sheet 2 Fig 4. /Z

i i; 1.2 Lamp 4- -17 Lead Lamp 6" Q Irwervcors: Raymond L. KePF'f'er,

fjgene 'Lemmers, 9 MC" Their At'korneg.

Patented June 30, 1953 PREHEAT NEUTRALIZING CIRCUIT FOR FLUORESCENTLAMPS Raymond. L. Keifier, Chagrin Falls, and Eugene Lemmers, ClevelandHeights, Ohio, assignors to General Electric Company, a corporation ofNew York Application November 23, 1949, Serial No. 129,158

This inventionrelatesgenerallyto starting and operating circuits forelectric discharge devices such as fluorescent lamps, and moreparticularly to a new and improved switchless circuit and transformerstructure for preheating the filamentary electrodes of such lamps atstarting, and for eliminating the heating current after the dischargehas started within the lamps.

Circuits presently in commercial use for operating fluorescent lampsare-generally provided, either with switching means to allow preheatingof the lamp electrodes to an'electron-emitting temperature, or with highvoltage high leakagereactance transformers to start the lamps directlywithout any preheating of the electrodes. The first method of operationnecessitates an undesirable delay in starting the lampafter the initialapplication of voltage to the circuit, and often results in undesirableflickering when the lampfails to start on the first attempt; the secondmethod places considerable electrical stress Claims. (Cl. 315===95) onthe lamp electrodes which, other factors being equal, results in ashorter lamp life.

In our copending United States application No. 731,488 (Lemmer-s andKeiff'er), filed February 28, 194"], now U. S. Patent 2,504,549,assigned to the same assignee as the present invention, there isdisclosed a circuit for impressing heating voltages across thefilamentary electrodes of a fluorescent lamp at'starting, which circuitcomprises three windings per electrode for neutralizing these voltagesthrough changes in phase and magnitude of currents through a transformerconsequent upon conduction in the lamps.

The present invention utilizes basically the same principles asdescribed in the aforementioned application, and is concerned withanimproved and more economical circuit and transformer structure forelectrode preheating and subsequent neutralization in a like manner,wherein the number of windingsper electrode is substantially reduced.

Accordingly, it is an object of our invention to provide an improved andsimplified circuit for switchless starting and operation of fluorescentlamps, which permits the application of heating voltages to thefilamentaryelectrodes of such lamps previous to st-artingand which,immediately upon initiation of a'discharge within said lamps,discontinues said heating voltages by means of changes in the phases andmagnitudes of'their components seats to substantially neutralize them.

Another object of our invention is to provide an improved circuit foreffecting the first-mentioned object and which, in addition, is welladapted to'extension'to any number. of lamps by the simple expedient ofmultiplying the windings on an auxiliary transformer.

A further object of our invention is to provide a circuit which, inadditionto fulfilling the previously mentioned objects, is particularlyadaptable to certain modifications for providing a starting voltage toan auxiliary electrode, which starting voltage is likewise neutralizedafter the lamps have started, in the same manner as the heatingvoltages.

For further objects and'advantages and for a better understanding'of ourinvention, attention is now directed to the following description and tothe accompanying drawings. The novel features of our invention will bemore clearly pointed out in the appended claims.

In the drawings:

Fig. l is'a schematic diagram of a starting and opera-ting circuit for apair of fluorescent lamps embodying our invention.

Figs. 2'and 3 are vector diagrams for the purpose of illustrating thevoltage relationships in the windings of the transformer of Fig. 1,under starting and operating conditions, respectively.

Fig. 4 is aschematic diagram of a modified form of our neutralizingcircuit as applied to a low reactance transformer of well known design.

Fig. 5 is a diagrammatic representation of a transformer structureembodying certain featuresof my invention.

Referring to Fig. 1 there is shown a pair of electric discharge devicesI, I such as fluorescent lamps, which will be referred to henceforth asthe lag lamp and the lead lamp respectively. These lamps compriseelongated tubular or cylindrical envelopes 2, 2', which have sealed intotheir ends filamentary electrodes 3, 4, and 5, 6, respectively. Theseelectrodes may be constituted by coils of tungsten wire activated withoxides of alkaline earth metals, such as barium and strontium oxides.The envelopes 2, '2' contain rare gases such as krypton, neon, argon, ormixtures thereof, at a pressure of'a few millimeters, and a smallquantity of mercury. The devices I, I may be low pressure, positivecolumn lamps of the fluorescent type, provided with a suitable phosphorcoating. This fluorescent coating, upon excitation by the radiationproduced by an elec tric discharge between the electrodes, transforms ashort wave length radiation due to the dis charge, into a longer wavelength radiation occurring within the visible range.

The lamps l, i are connected in a lagging power factor load circuit 1, Band a leading power factor load circuit 9, 8, respectively, whichcircuits are connected across a suitable source of potential. In thedrawings; we have illus trated a voltage step-up autotransformer ill,comprising a primary winding ii and a pair of secondary windings l2 andi3. The secondary windings are loosely coupled to the primary windingand have considerable leakage react" ance; such a structure isrelatively well known in the art, and permits utilization of thesecondary windings both as voltage step-up windings, and as ballastreactances for limiting the discharge current through the lamps. The laglamp is connected directly through conductor 1 to secondary winding l2,whereas the lead lamp is connected through its conductor 9 to winding[3, in series with a capacitor [4 which performs the usual function ofinverting the total reactance in this part of the circuit from inductiveto capacitive.

In accordance with the principles disclosed in our application No.731,488, voltages for heating the filamentary electrodes of the lampsmay be provided by means of three sources, these sources havingpredetermined phase relations which change upon the initiation of adischarge through the lamps. In the above-mentioned application, we haveshown three teritary windings, coupled to the three windings ofautotransformer 12, for each of the four filamentary electrodes. Inother words, three tertiary windings are required for each lampelectrode so that for the two lamps illustrated herein, four groups ofthree tertiary windings, that is, a total of twelve teritary windingsare required.

In accordance with our present invention, the number of tertiarywindings is greatly reduced. Associated with each winding ofautotransforrner I is a single tertiary winding, these tertiary windingsbeing l5, l6, and H for windings ll, l2, and [3, respectively. The threetertiary windings are connected in series across the primary winding [8of an auxiliary transformer iii, which transformer will be referred tohenceforth as the cathode heating transformer. Transformer 19 may be ofconventional construction, and is provided with as many secondarywindings as there are filamentary electrodes which it is desired toheat. As illustrated herein, transformer I9 is provided with secondarywindings 20, 2|, 22, and 23 for electrodes 3, 4, 5, and B, respectively.

The turns of the tertiary windings in autotransformer l2 are soproportioned that a result voltage is impressed across primary iii ofcathode heating transformer l9 at starting of the lamps, and thisvoltage is substantially neutralized after a discharge has started inthe lamps. It will be obvious to those skilled in the art that it isthereafter a relatively simple matter to design cathode heatingtransformer IS to have the secondary windings thereof transform theapplied voltage to any desired value of volt age for heating the lampelectrodes, or for performing other functions.

Referring to Figs. 2 and 3, the vector diagrams therein illustrate thephase and magnitudes of the voltages in the tertiary windings ofautotransformer i2, Fig. 2 being applicable to the voltage existingbefore starting, and Fig. 3 being applicable to voltages existing duringlamp operation.

When the supply voltage is initially applied across primary winding llof autotransformer it, the induced voltages in secondary windings l2 andit are practically in phase with the voltage existing across the primarywinding, and there is no discharge current circulating through windingsI2 and [3 to disturb these phase relationships. Accordingly, thevoltages induced in tertiary windings I5, 15, and I? are in like phaseand may be represented by vectors V15, V16, and Viv, respectively. Thesevoltages add up to produce the resultant V7 which has a mag nitude,after conversion through the cathode heating transformer I9, sufiicientto cause heat ing of the filamentary electrodes in the lamps.

After the lamps have attained an electronemitting temperature, the arcor discharge strikes within them; and the phases of the currents throughthe secondary windings i2 and H are respectively retarded and advanced.This is due to the fact that the leakage reactance of winding l2introduces an inductive reactance in series with lag lamp I, whereascapacitor [4 introduces a capacitive reactance in series with lead lampl which overcomes the leakage reactance of secondary winding 13. Thephases of the voltages induced in tertiary windings l6 and I! areretarded and advanced respectively in the same fashion as the currentsthrough secondary windings I2 and I3, and the voltage induced intertiary winding l5 naturally remains unchanged. Accordingly, thevoltages in the tertiary windings may be represented by vectors V15,V16, and V17, of fig. 3 and these now add up vectorially to produce aresultant Vrcf substantially diminished magnitude.

In practice, complete neutralization is diflicult to obtain because ofthe potential drop in the filamentary electrodes of the lamp produced bythe arc or discharge current; the resultant voltage Vr', however, issmall enough to be negligible. In fact, perfect correlation between themagnitudes and phases of the voltages in the tertiary windings to obtainsubstantially zero resultant voltage during lamp operation is notnecessary for the successful operation of the circuit, and a smallamount of residual electrode-heating current is often desirable in orderto lower the cathode voltage or are drop.

Referring once more to Fig. 1, there is shown, in cathode heatingtransformer 19, an auxiliary secondary winding 24, illustrated in dottedoutline. This winding may be utilized, if desired, to provide a startingvoltage to a pair of auxiliary electrodes 25, 25' in the lamps. Theseelectrodes may be constituted by stripes of conductive metallic paintapplied to the surfaces of envelopes 2 and 2 of lamps l, l,respectively. The uses and principles of operation of such auxiliarystarting electrodes are well known in the art and need not be describedexcept to state that they permit a lowering of the starting voltagerequired across the main electrodes. It will be apparent that byobtaining the auxiliary starting voltage from cathode heating transformer I9 in accordance with our invention, the starting voltage isremoved from the stripes or auxiliary electrodes as soon as thedischarge is started within the lamps. This is due to the fact that thestarting voltage is neutralized in exactly the same fashion as theheating current to the filamentary electrodes. This is a noteworthyfeature since it is generally advantageous to remove high voltages fromcircuits with which operating personnel may come into contact.

.Although the circuit has thus far been described. referencetosxahighleakage reactance type of transformer, wherein. the-.balla-sti-naction. required. for ,rlimiting the: discharge current. through the.lamps; iss providedv by the secondary windings: of. the step-uptransformer; the circuit is equally applicable to a: low reactance typeofastep-up transformer. Such a circuit is illustrated iii-Fig. a,whereinlsimilar reference numerals refer to corresponding elements.Thus, referring to Fig; .4, step-up autotransformer Hi comprises, asbefore, apri'mary winding II, but this winding is now, continued intov atightly coupled section H. which providesa voltage step-up action.Connected tothe outer end of section I lare separate ballastingreactances t2 and It, reactance l2 beingconnected directly, andrea-ctance t3 being connected. through theusual phase advancingcapacitor Mp The electrode heating andneutraliz-in-g windings l5, l6,and I! are coupled to windings II, It, and. I3, respectively, theremainder of the circuit being in all other, respects similar to thatof-qFig. 1-.

The 'loperation of this c-ircuitis likewise similar to that of Fig. 1.The voltage for heating the lamp electrodes at starting is generatedwinding 15. After the discharges have started, the voltages induced inwindings l6 and I! by the discharge current' fiowing through ballastreactances l2 and. I3 add vectorial-ly to the voltage induced in windingii to produce a resultant of substam tiallyzero magnitude, therebyneutralizingthe electrode heating. 'Cathodeheating transformerl9provides the required transformationforapplying the resultant of theinduced voltages to the various lamp electrodes.

Fig. his a diagrammatic representation of a transformer, similar to thatdescribed in appli= cation No. 690,855 of Charles W. Kronmiller, filedAugust 16,, 19416, and assigned to the same assignee as the presentinvention. The transformer herein is adapted to provide the windingsrequired by the circuit of Fig. "I, and similar re er= ence numeralsrefer to corresponding circuitelements. Transformers Hi and Idcomprise'a'com mon core 26; the transformer structure built upon core 26to the right of section line 21-2? consti= tutes transformer l6, whilethe structure to the left of the section line constitutes transformer19. Primary winding H and secondary winding l2 and 13 are mounted inseparate slots in core members 28 and 28; and tertiary windings l5, l6,and H are likewise mounted in these slots in close coupling with theirassociated main windings. Air gaps 29, 30, and 3! provide the desiredleakage reactance between main windmgs.

The windings I8, 20, 2!, 22, 23, and 24 of trans= former H! are mountedin a slot in core members 32 and 32'. An air gap 33 provides thenecessary magnetic decoupling between transformers l9 and 10. It is tobe understood that this particular transformer structure is given simplyby way of non-limitative illustration; and, obviously, separatetransformer structures may be utilized if desired.

While certain specific embodiments have been shown and described, itwill, of course, be understood that various modifications may be madewithout departing from the invention. Thus, it will be obvious that thecircuit may be modified to include any number of lamps by providing twoadditional secondary windings for the electrodes of each additionallamp. Likewise, whereas we have shown particular circuits comprising astepup autotransformer, it will be evident that other circuits whichproduce likeresults may be used in lien or the one which has been:illustrated by adding: tertiary windings. to it in! the manner described in our invention. :Theappended claims are, therefore, intendedto cover any such modifications coming within the true spirit and scopeof the. invention.

What we claim as new and desireto secure by Letters Patent of. theUnited States is: I

1'. Apparatus'for starting and operating electric discharge devices ofthe type including a pair of thermionicelectrodes, comprising; a primaryinductance adapted for connection to an alter mating-current supply, anda pair of secondary inductances connected to said primary inductance forlimiting the currentsupplied toalaggi-ng and to -a leading power-factorload circuit each illeludingone of said devices; three tertiarywindings, separate onesof. said tertiary windings being coupled tosaidprimary and secondary inductances; said tertiary/windings beingconnected in series and poled for producing a resultant voltagethemagnitude of which varies with the cunrent conducted by said secondaryi-nductances, and auxiliary transforming means comprising a primarywinding connected across said.- tertiary windings in series and alsoincluding a plurality of secondary windingsadapted to be connected tothe electrodes of said discharge devices for providing heating currentthereto.

2. Apparatus for starting and operating electric discharge devices ofthe type including a pair of thermionic electrodes, comprising: amagnetic core structure having'wound thereon a primary winding adaptedfor connection to an alternating currentsupply, and a pair of secondarywindings inductively coupled to said primary winding with high leakagereactance in said core structure therebetween, and connected to saidprimary winding for limiting the current supplied to a lagging and toa'leading power factor load circuit each including one of said devices;three tertiary windings'separate ones of said tertiary windings beingcoupled to said primary and secondary windings, said tertiary windingsbeing connected in series and poled for producing a resultant voltagethe magnitude of which varies in accord= ance with the current conductedby said secondary windings; and auxiliary transforming means comprisinga primary winding connected across said tertiary windings in series, anda plu= rality of secondary windings adapted to be con= nected to theelectrodes of said discharge devices for providing heating currentthereto.

3. Apparatus for starting and operating electric discharge devices ofthe type including a pair of thermionic filamentary electrodes,comprising: a magnetic core structure having wound thereon a primarywinding for connection to an alternating current supply, and a pair ofsecondary windings connected to said primary winding, and inductivelycoupled thereto with high leakage reactance in said core structuretherebetween for limiting the current supplied to a lagging and to aleading power factor load circuit each including one of said devices;three tertiary windings, re spective ones of said tertiary windingsbeing inductively coupled to said primary winding and to said secondarywindings, the tertiary winding coupled to said primary winding producinga reference voltage, and the tertiary windings coupled to said secondarywindings producing components of voltage variable in magnitude and phasein response to currents conducted by said secondary windings, saidtertiary windings being connected in series and poled so that theresultant of said reference voltage and said components is reduced uponthe flow of current through said secondary windings; and an auxil iarytransformer comprising a primary winding connected across said tertiarywindings in series for receiving said resultant voltage, and secondarywindings coupled thereto for converting said resultant to voltages ofdesired amplitude adapted to be applied to the electrodes of saiddischarge devices for providing heating thereof at starting.

4. Apparatus for starting and operating electrio discharge devices ofthe type including a pair of thermionic filamentary electrodes and anaux= iliary starting electrode, comprising: a magnetic core structurehaving wound thereon a primary Winding for connection to an alternatingcurrent supply, and a pair of secondary windings con nected to saidprimary inductance, and coupled thereto with high leakage reactance insaid core structure therebetween for limiting the current supplied to alagging and to a leading power factor load circuit each including one ofsaid devices; three tertiary windings, respective ones of said tertiarywindings being inductively coupled to said primary winding and to saidsecondary windings, the tertiary winding coupled to said primary windingproducing a reference voltage, and the tertiary windings coupled to saidsec ondary windings producing components of volt age variable inmagnitude and phase in response to the currents conducted by saidsecondary windings, said tertiary windings being connected in series andpoled so that the resultant of said reference voltage and saidcomponents is reduced upon the flow of current through said secondarywindings; and an auxiliary transformer com= prising a primary windingconnected across said tertiary windings in series for receiving said resultant voltage, secondary windings coupled thereto for converting saidresultant to voltages of desired amplitude adapted to be supplied to theelectrodes of discharge lamps for heating thereof at starting, and anauxiliary winding coupled thereto for converting said resultant to avoltage of desired amplitude adapted to be applied to said startingelectrodes.

5. A transformer structure comprising: a magnetic core, primary andsecondary windings on said core, said windings being loosely coupled bymeans of a leakage flux path therebetween; connection linking saidwindings in autotransformer relation for providing a relatively highopen circuit voltage and a relatively low operating voltage when loadcurrents flow therethrough to associated leading and lagging circuitsfor operating discharge devices of the filamentary electrode type; threetertiary windings mounted on said core, separate ones of said windingsbeing closely coupled respectively with said primary and secondarywindings, said tertiary windings being connected in series andpoled toproduce a resultant voltage the magnitude of which decreases with thecurrent conducted by said secondary windings; and auxiliary windingsmounted on said core, said auxiliary windings being relatively decoupledfrom previously mentioned windings by means of high leakage flux paths,said auxiliary windings comprising an auxiliary primary windingconnected across said tertiary windings in se ries for receiving aresultant voltage having a substantial value when no load current flowsin said primary and secondary windings and having a lesser value whenload currents flow therein, and auxiliary secondary windings closelycoupled to said auxiliary primary winding for converting said resultantvoltage to voltages of predetermined amplitude for application to theelectrodes of said devices to provide heating thereof.

RAYMOND L. KEIFFERi EUGENE LEMMERS.

References Cited in the file of this patent, UNITED STATES PATENTSNumber

